A multifactorial risk pattern of periodontitis has been recognized, where in addition to host and environmental factors a pathogenic microbiota plays a primary role. At present no definite answer can be given to the question of whether the expression of either aggressive etiological agents (implying infection with a virulent microbiota), or a high level of individual susceptibility to periodontal disease, or a specific combination of both is the conductive factor in the etiopathogenesis of aggressive periodontitis. The purpose of the current research was to analyze the prevalence of periodontitis-associated microorganisms in patients with aggressive periodontitis and periodontally healthy elders by using molecular-biologic detection methods like eubacterial PCR-amplification of 16S rDNA in combination with dot-blot hybridization. The oligonucleotide probes for the detection of Tannerella forsythensis, Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, Campylobacter rectus, Fusobacterium nucleatum, Fusobacterium spp., Prevotella intermedia, Eikenella corrodens, Veillonella parvula and Capnocytophaga ochracea were designed and evaluated. The PCR products of 42 cultivated target and closely related bacteria were obtained for the optimization of hybridization conditions. For the epidemiological study subgingival plaque was sampled from four pockets and one healthy site of 45 aggressive periodontitis patients as well as from five sites of 21 elderly. The differences in the prevalence of bacterial species was analyzed by chi-square test. The results of the study confirmed the reliability of the oligonucleotide probes in a specific and sensitive detection of the respective oral species. The data of the epidemiological study revealed frequent colonization by T. forsythensis, P. gingivalis, F. nucleatum and C. rectus in patients with aggressive periodontitis, however individual variations were obvious. These microorganisms could be predominantly identified in periodontal pockets, but were significantly less common in the healthy sites of the periodontitis patients and in the elderly subjects. A. actinomycetemcomitans could be detected in only a few patients, reducing its suspected importance in the etiopathogenesis of aggressive periodontitis. No direct association for P. intermedia and E. corrodens with aggressive periodontitis or periodontal health could be seen. C. ochracea was highly prevalent in the well-maintained elderly, being rarely found in the diseased group. The putative pathogens T. forsythensis, P. gingivalis, F. nucleatum and C. rectus can be conclusively suggested as the key-bacteria in patients with aggressive periodontitis. However, considering that periodontitis is a polymicrobial infection, the screening of the microbial population, rather than the isolation of single members of the subgingival flora, should give a more comprehensive perspective in etiopathogenetic research of periodontitis.

Fig. 1 Bar chart showing the prevalence of the respective species in 44 GAP patients (one GAP patient was excluded because of a missing control site) and 21 elderly subjects. A patient was regarded positive when at least one site harbored the respective species. The significance of differences between the groups was calculated using the chi-square test.

Fig. 2. Percent of positive periodontal pockets and control sites in 44 GAP patients. The significance of differences was evaluated using the chi-square test.

Fig. 3. Site-prevalence of the species in 45 GAP patients and 21 elderly (4 sites per subject were included). The significance of the differences between the groups was determined using the chi-square test.

Fig. 4. Comparison between the colonization of shallow sites (PD 1-3 mm) in 44 GAP patients and 17 elderly. Only one site per subject could be included. The significance of differences was evaluated using the chi-square test.

Fig. 5. Bar chart of the percent of positive sites with probing depth 1-3 mm, 4-7 mm and 8-12 mm in GAP patients (n=23). The significance of differences was determined using the chi-square test.

Fig.6. The bars depict the percent of subjects with either 0, 1, 2, 3 or 4 positive sites for T. forsythensis, P. gingivalis, F. nucleatum, P. intermedia, E. corrodens and C. ochracea in GAP group (n=45) and elderly (n=21). The significance of differences between the groups were determined using the Mann-Whitney test.